1. Field of the Invention
The present invention relates to an ultrasonic motor.
2. Description of the Related Art
In configuring an ultrasonic motor for generating elliptical vibrations on a vibrator by having a phase difference in vibration mode between different vibration modes by degenerating the different vibration modes, it is necessary to have a device for degenerating the different vibration modes. The device can be the following method proposed by patent document 1 (Japanese Laid-open Patent Publication No. 2006-94591).
This method is to regard the increase in the resonant frequencies of the two different vibration modes “longitudinal vibration mode” and “flexional vibration mode” when pressure is applied to a vibrator, and the inclination of the increase of the resonant frequency of the flexional vibration mode as being higher than the inclination of the increase of the resonant frequency of the longitudinal vibration mode. That is, a difference in resonant frequency is to be maintained between the two vibration modes before the application of the pressure so that the resonant frequencies can substantially match each other when predetermined pressure is applied.